The subject matter disclosed herein relates generally to fuel systems, and, more specifically, to cooling flow recirculation in fuel manifolds, such as fuel manifolds associated with gas turbine engines.
Low emissions combustion may utilize pilot and main fuel flow circuits within a fuel nozzle. The pilot and main circuits of the fuel nozzle may each be fed by a separate pilot and main fuel manifold, respectively. There are engine operation conditions that require the main flow through the nozzles to be turned off. In such cases, reference is made to cooling a non-flowing fuel manifold. The problem: When some fuel circuits are flowing fuel and other circuits are not flowing fuel, there may be a risk of coke formation in the non-flowing circuit. For example, main flow off operation may present a risk of coke formation in the main fuel circuit. One solution to this concern is to provide cooling flow through the main circuit during pilot only operation. Prior approaches have either added significant weight and consumed needed engine envelope or resulted in unwanted fuel dynamics and limited the ability to turn on the main flow. For example, some approaches have utilized recirculation back to the pump inlet. A downside to this approach is that it requires another fitting on the nozzle, requires routing through an engine strut, and adds weight. Additionally, utilization of recirculation back to the pump inlet makes it difficult to find necessary undercowl space in implementation. This and other approaches in the art have been shown to raise concerns relative to fuel flow dynamic response, as such dynamic response can cause engine operability problems and additional challenges regarding an inability to satisfactorily flow the main fuel circuits at low total metered flows.